Progressive spectacle lenses, also called Progressive Addition Lenses (PAL), progressive power lenses, graduated prescription lenses, Progressive Lenses and Varifocal or multifocal lenses, are corrective lenses usually used to correct disorders on the eye's ability to change focus to see near objects clearly.
The progressive lenses are often referred to as no-line bifocals. Bifocal lenses contain portions for near and distance vision, separated by a distinct line. Bifocal lenses bring the vision into focus when looking at a far distance and bring the near vision into focus when viewing close objects, without having to take the glasses on or off. The progressive lenses contain the different viewing portions, but have no visible lines to separate the viewing portions. Instead, progressive lenses have an upper distance portion (‘the distance zone’), a lower near portion (‘the near zone’), and a progressive corridor (‘the intermediate zone’) there between which provides a gradual power progression from the distance zone to the near zone. The progressive lenses may be characterized by the gradient of increasing lens power.